Top 10 Java String interview questions and answers

1.How many ways we can create string in java ?

There are two ways in which we can create string in java.

1 By String literal

2. By new Keyword

1.By string literal

String name=”placement”;

2.By new keyword

String name=new String(“placement”);

2.What is the difference between the StringBuffer and StringBuilder ?

StringBuffer:

StringBuffer is synchronised that means thread safe.

It is less faster than StringBuilder

StringBuilder:

StringBuilder is non-synchronised that means non-thread safe.

It is more faster than StringBuffer

3.What do you mean by Immutable and mutable objects ?

Immutable objects

Immutable objects simply refers the object whose value can not be changed.

It is like a constant objects ie final

mutable objects

mutable objects simply refers the object whose value can be changed.

It is like not a constant objects

4.How can you convert string into a char array ?

Using toCharArray( ),we can convert string into a sequence of character.

The length of string will same as length of character array.

Example

class StringtocharArray
{
public static void main(String[ ] args)
{
String s=”placement”;
char [ ] charArray=s.toCharArray( );

for(int i=0;i<charArray.length;i++)
{
System.out.print(charArray[i]+” “);
}
}
}

Output:

[ p l a c e m e n t ]

5.What is the difference main difference between the equals( ) method & == operator ?

equals( ) method 

1.equals( ) is method 

2.It compare the string on the basis of original content.

3.Example

public class EqualsMethod
{
public static void main(String[ ] args)
{
String s=”placement”;
String s1=new String(“placement”);
String s2=”placement”;

System.out.println(s.equals(s2));// true
System.out.println(s1.equals(s2)); // false
}
}

Output:

true

false

== operator

1.== is an operator

2.It compare the string on the basis of reference(address)

3.Example

public class DoubleEqualOperator
{
public static void main(String[ ] args)
{
String s=”placement”;
String s1=new String(“placement”);
String s2=new String(“placement”);

System.out.println(s1==s2); //true
System.out.println(s==s2); //false
}
}

Output:

true

false

6.How can you remove all white spaces from String in java ?

We can remove all white space from string in java using replaceAll( ) method.

Example:

public class RemoveWhiteSpace
{
public static void main(String[ ] args)
{
String name=”This is placement preparation”;
//using replaceAll( ) method
name=name.replaceAll(“\\s”,””);
System.out.println(name);
}
}

Output:

Thisisplacementpreparation

7.How many objects will  be created in the given below code ?

String s=”placement”;

String s1=”placement”;

According to,string pool concept

Only one object will create

8.Why string is thread-safe in java ?

Because strings are immutable, which means it value can’t be changed in a program & also it is used  in a multi-threading environment so it is thread-safe.

9.How can you convert String into integer and integer into String in java ?

We can convert string into integer using Integer.ParseInt( ).

int number=Integer.ParseInt(“10”);

We can convert integer into a string using Integer.toString( ).

String s=Integer.toString(number);

10.Is string a primitive or a Derived data type ?

A string is a primitive data type which has state and behaviour.some methods of strings are subString( ) ,indexOf( ) etc.

It is stored in a special region called string pool.

Thanks and Regards

Placement preparation

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